Method and system for diagnostics of a particulate matter sensor

ABSTRACT

A diagnostic method and system is described for diagnosing an operating condition of a conductive particulate matter sensor. The sensor has a substrate and two electrodes on the substrate adapted to collect particulate matter between the electrodes, thereby establishing an electrically conductive path through collected particulate matter between the electrodes that can be detected by measuring electrical resistance between the electrodes, R elect . The diagnosis is performed by detecting whether water vapor condensate may be present between the electrodes and if it is, then measuring resistance between the electrodes while subjecting the sensor to conditions sufficient to evaporate any water vapor condensate and diagnosing a validation that the sensor is in proper operating condition if resistance increases in a manner consistent with evaporation of condensate.

BACKGROUND OF THE INVENTION

This invention relates generally to sensors for detecting electricallyconductive particulate matter, such as soot, and more particularly to amethod and system for diagnosing potential failure modes in suchsensors.

Incomplete combustion of certain heavy hydrocarbon compounds, such asheavy oils, diesel fuel, and the like may lead to particulate formation(e.g., soot). In the operation of internal combustion engines, excessiveparticulate formation can lead to “smoking” of the engine, which causesair pollution even though the carbon monoxide, hydrocarbons, and otherpollutant components of the gaseous state exhaust emissions may berelatively low. Emission regulations require many engines to limit thelevels of particulate emissions, and various control technologies suchas diesel particulate filters (DPF) have been employed for this purpose.

In order to monitor the emission of particulate matter in the exhauststreams of certain types of internal combustion engines, e.g., to assessthe effectiveness of DPF's, it is known to provide a particulate sensorsystem for detecting the level of particulate concentration emitted froman exhaust gas. Various particulate sensors have been proposed,including those shown in U.S. Pat. No. 4,656,832 issued to Yukihisa etal., U.S. Pat. No. 6,634,210 issued to Bosch et al., U.S. Pat. Publ. No.2008/0283398 A1, U.S. Pat. Publ. No. 2008/0282769 A1, and U.S. Pat.Publ. No. 2009/0139081 A1, the disclosures of each of which are herebyincorporated by reference in their entirety.

Particulate sensors such as those described above generally have a pairof spaced apart sensing electrodes disposed on a substrate. The sensingelectrodes are coupled to a measurement circuit by way of electricallyconductive leads. The operating principle of the particulate sensor isbased on the conductivity of the particulates (e.g., soot) deposited on(or over) the sensing electrodes. The electrical resistance between thesensing electrodes is relatively high when the sensor is clean but suchresistance decreases as soot particulates accumulate. These sensors alsohave a heater that can be selectively activated to burn off the sootparticulates to “reset” the sensor to a known, base “clean” state.

However, for diagnostic purposes, it can be difficult to distinguishbetween various states that may occur during various engine operatingconditions, such as between: (i) a faulty state such as when there is anelectrical open circuit in the wiring leads, which presents as a veryhigh resistance between the sensing electrodes, and (ii) a normal state,such as when a sensor has just been cleaned, which also presents as avery high resistance, or between (i) a false positive state such aswhere the sensor presents a low resistance due to some cause other thansoot particulates, e.g., water vapor condensate on the electrodes, and(ii) an actual positive state such as where soot particulates on theelectrodes lead to a low resistance measurement.

Accordingly, there is a need for particulate sensor diagnostics that canaccurately distinguish between sensor states during various engineoperating conditions.

SUMMARY OF THE INVENTION

The present invention relates to a method and system for diagnosing anoperating condition of an electrically conductive particulate mattersensor having a substrate with two electrodes on the substrate adaptedto collect particulate matter between the electrodes, therebyestablishing an electrically conductive path through collectedparticulate matter between the electrodes that can be detected bymeasuring electrical resistance between the electrodes, R_(elect).

This method comprises the steps of:

-   -   (a) detecting whether water vapor condensate may be present        between the electrodes;    -   (b) if water vapor condensate may be present between the        electrodes, subjecting the sensor to conditions sufficient to        evaporate any water vapor condensate, and detecting whether        R_(elect) increases in a manner consistent with evaporation of        water vapor condensate;    -   (c) if step (b) detects that water vapor condensate may be        present, and if R_(elect) increases in a manner consistent with        evaporation of water vapor condensate in response to the sensor        being subjected to conditions sufficient to evaporate any water        vapor condensate, then diagnosing a validation that the sensor        is in proper working condition.

In certain exemplary embodiments of the invention, although it is notrequired, a secondary diagnostic method may be used to account for caseswhere the above-described method determines that water vapor condensateis not present between the electrodes, or if R_(elect) does not increasein a manner consistent with evaporation of water vapor condensate. Inone exemplary embodiment, such a secondary diagnostic method comprisesthe steps of:

-   -   (d) if water vapor is not detected between the electrodes in        step (a), or if R_(elect) does not increase in a manner        consistent with evaporation of water vapor condensate in step        (b), then providing heat to the sensor in an amount sufficient        to modify the electrical resistance of the substrate, and        detecting whether R_(elect) changes in a manner consistent with        heating of the substrate;    -   (e) if R_(elect) increases in a manner consistent with heating        of the substrate in step (d), then removing the heat provided in        step (d) to cool the substrate;    -   (f) if R_(elect) does not change in a manner consistent with        heating of the substrate in step (d) or R_(elect) does not        change in a manner consistent with cooling of the substrate in        step (e), then diagnosing a failure condition for the sensor;        and    -   (g) if R_(elect) changes in a manner consistent with cooling of        the substrate in step (e), then diagnosing a validation that the        sensor is in proper working condition.

Exemplary embodiments of the invention also relate to a storage mediumencoded with machine readable computer program code for diagnosing afailure condition of an electrically conductive particulate mattersensor as described above where the storage medium includes instructionsfor causing a computer to implement the above-described method.

Another exemplary embodiment of the invention relates to a diagnosticsystem for an electrically conductive particulate matter sensor asdescribed above, the system comprising a microprocessor in communicationwith the sensor and a storage medium including instructions for causingthe microprocessor to implement the above-described a method.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a top end view of a sensing element end useful in a sensor forwhich the diagnostics of the invention may be practiced.

FIG. 2 is a schematic showing an exemplary sensor for which thediagnostics of the invention may be practiced.

FIG. 3 is a circuit diagram showing a circuit for measuring resistancebetween electrodes of a particulate matter sensor.

FIG. 4 is a schematic illustration of an engine control module and aparticulate matter sensor.

FIG. 5 constitutes a schematic illustration of a flow chart illustratingportions of a control algorithm contemplated for use in exemplaryembodiments of the present invention.

FIG. 6 constitutes a schematic illustration of a flow chart illustratingportions of a control algorithm contemplated for use in exemplaryembodiments of the present invention.

DETAILED DESCRIPTION

Referring now to the Figures, where the invention will be described withreference to specific embodiments, without limiting same.

In describing and claiming algorithms according to the invention,letters and naming conventions are arbitrarily employed to representnumerical values (e.g., R_(OBD) _(—) _(hot), K_(R) _(—) _(evap) _(—)_(thresh)). These naming conventions are used solely to enhance thereadability of the description of the invention, and are not intended tohave any functional significance whatsoever. The representation of thesenumerical values is intended to be precisely the same as if, for examplecompletely arbitrary descriptions (e.g., R₁, R₂, K₁, K₂) had been used.Additionally, it should be noted that in the practice of the invention,measurements of resistance between the electrodes may be made byapplying a known current across the electrodes, measuring the voltagedifferential between the electrodes, and calculating the resistanceusing Ohm's law, as is well-known in the art. It would of course bepossible to simply use the voltage values in place of resistance valuesin the algorithm of the invention by converting the various resistanceconstants and equations to voltage, and such alternative embodiments areconsidered to be within the scope of the invention.

FIG. 1 shows an exploded view of an exemplary particulate matter sensorthat can be used in the practice of the present invention. In general,the sensor comprises a sensing element and a heating element, whereinthe sensing element may comprise, but is not limited to, at least twosensing electrodes in proximity to each other on a substrate andconfigured so as to accumulate particulate matter therebetween, andwherein the heating element may comprise, but is not limited to, atemperature sensor, and a heater. The sensor may include a multi-layeredstructure comprising the sensing element, the temperature sensor, theheater, and a combination comprising at least one of the foregoing,contained in a single structure formed, e.g., by multi-layer technology.

The sensing electrodes can include metals, such as, gold, platinum,osmium, rhodium, iridium, ruthenium, aluminum, titanium, zirconium, andthe like, as well as, oxides, cermets, alloys, and combinationscomprising at least one of the foregoing metals. In an exemplaryembodiment, the sensing electrode can comprise a platinum/alumina cermetwherein the platinum is about 90 wt % (weight percent) to about 98 wt %of the sensing electrode. In another exemplary embodiment, the sensingelectrode comprises about 93 wt % to about 95 wt % platinum, whereweight percent is based on the total dry weight of the cermet. Eachsensing electrode may be composed of the same or different material asthe other sensing electrode(s).

The sensing electrodes can be formulated in any fashion. In oneexemplary embodiment, however, the sensing electrodes are formed byfirst preparing an ink paste by mixing an electrode forming-metal powder(e.g., platinum, gold, osmium, rhodium, iridium, ruthenium, aluminum,titanium, zirconium, and the like, or combinations of at least one ofthe foregoing) with oxides in a sufficient amount of solvent to attain aviscosity suitable for printing. The oxides used to form the sensingelectrodes may include those oxides that do not promote the oxidation ofparticulates and that do not lower the burn-off temperature of theparticulates. Non-suitable oxides are, e.g., copper oxide, cerium oxide,and iron oxide. The ink paste forming the sensing electrode can then beapplied to an electrode substrate via sputtering, chemical vapordeposition, screen printing, flame spraying, lamination, stenciling, orthe like.

The sensing electrodes may be disposed onto the electrode substrate suchthat a constant distance of separation between each sensing electrode iscreated. The width of the distance separating the sensing electrodes canvary widely, depending upon desired design parameters. In one exemplaryembodiment, this distance comprises a width of separation of about 0.01to about 0.12 millimeter (mm).

Both the heater and the temperature sensor, forming in whole or in part,the heating element, can comprise various materials. Possible materialsinclude platinum, gold, palladium, and the like; and alloys, oxides, andcombinations comprising at least one of the foregoing materials, withplatinum/alumina, platinum/palladium, platinum, and palladium. Theheater and temperature sensor can be applied to the sensor in anyfashion, such as by sputtering, chemical vapor deposition, screenprinting, flame spraying, lamination, and stenciling among others. Inone embodiment, the heater can comprise a thickness of about 3 to about50 micrometers. In another embodiment the heater thickness is about 5 toabout 30 micrometers. In yet another embodiment, the heater thickness isabout 10 to about 20 micrometers.

The sensor may further comprise various substrates useful inelectrically isolating and protecting the sensing element and theheating element from the temperature surrounding the sensor and/or fromthe thermal reduction of the condensed particulates during theself-regeneration cycles. The substrates include, but are not limitedto, an electrode protective layer, an electrode substrate, an isolationlayer, an insulating temperature substrate, a heater substrate,insulating substrates, wherein the number of insulating substrates issufficient to prevent disruptive ionic or electrical communicationbetween the heating element and the sensing electrode (e.g., about 2 toabout 3 insulating substrates), and combinations comprising at least oneof the foregoing.

The substrates can comprise non-ionically conducting, electricallyinsulating materials. Possible electrically insulating materials includeoxides, such as alumina, zirconia, yttria, lanthanum oxide, silica, andcombinations comprising at least one of the foregoing, or any likematerial capable of inhibiting electrical communication and providingphysical protection. In order to hinder electrical communication betweenthe components of the sensor, the substrates may be composed of a highpurity oxide; e.g., less than about 10.0 wt % impurities. In anotherembodiment, the substrates comprise less than about 8.0 wt % impurities.In yet another embodiment, the substrates comprise less than about 5.0wt impurities, wherein the weight percent of the impurities is based onthe total weight of the substrate. Although the composition of theindividual substrates can vary, in certain embodiments they comprise amaterial having substantially similar coefficients of thermal expansion,shrinkage characteristics, and chemical compatibility in order tominimize, if not eliminate, delamination and other processing problems.Alkaline (e.g., sodium, potassium, lithium, and the like) oxides shouldbe avoided as they can be easily reduced to form impurities in theheater, temperature sensor, and the sensing electrodes.

In general, each of the substrates can be of sufficient size to supportthe entire length of the sensing electrodes, the temperature sensor,and/or the heater. The thickness of each substrate can be determinedbased on the desired thermal response time of the self-regenerationcycle, where shorter thermal response times require a smaller thickness.The thickness of each substrate can be up to about 200 micrometersthick. In an exemplary embodiment, the substrate thickness is about 50to about 180 micrometers. In another exemplary embodiment, the substratethickness is about 140 to about 160 micrometers. The substrates can beformed using ceramic tape casting methods, and the like.

Any number of the substrates can be porous, dense, or both porous anddense. The porosity or the diameter of the pores can be controlled tolimit the various sizes of particulates that can reach the sensingelectrodes, and to limit the size of particulates that can penetrate andtrap within the porous layer. In general, larger-sized particulates(e.g., particles having a diameter along the major axis equal to orgreater than about 5 micrometers) interfere with current conduction morethan do smaller-sized particulates (e.g., particles having a diameteralong the major axis less than about 5 micrometers). Therefore, wheremore precise conductance measurements are desired, it is especiallydesirable to exclude the larger particulates from accumulating onto orbetween the sensing electrodes. Such exclusion can be achieved bycontrolling the size and/or the number of pores on the substrate, and/orby controlling the internal tortuousness of the substrate. Here,tortuousness is defined as the effective path length through theconnected pores per standard thickness of the layer.

Pore size can be controlled by the size of the fugitive materials used,e.g., by controlling the size of carbon black or graphite, wherefugitive materials are those materials that burn off at hightemperatures leaving behind pores with controlled sizes. Tortuousnessdepends on the texture of the substrate-forming oxide powder used toform the substrate. Texture, in turn, can be controlled by firing thesubstrate-forming oxide powder at a high temperature to coarsen thesubstrate-forming powder, and then sieving the substrate-forming metalpowder to the right size range for slurry making.

The sensor may further comprise various leads responsible forelectrically communicating the sensor with the sensor circuit. One endof each sensing electrode, one end of the temperature sensor, and oneend of the heater may have a connecting point to which one end of atleast one lead may be attached. Each sensing electrode may beelectrically connected with at least one lead extending from one end ofeach sensing electrode; and the heater is electrically connected with atleast one lead extending from one end of the heater.

After acquiring the components of the sensor, the sensor may beconstructed according to thick film multilayer technology such that thethickness of the sensor allows for good thermal response time toward thethermal cycle of sensor regeneration. In an exemplary embodiment, thesensor element thickness is about 0.1 to about 3.0 millimeter (mm).

Referring now to FIG. 1, FIG. 1 shows a sensing element pad 28 on asubstrate 30 after a pattern 32 has been cut into the sensing elementpad 28 with an ablating device. It will readily be appreciated thatprior to ablating the portion of the sensing element pad 28 into whichthe pattern 32 is to be formed is a continuous solidparallelepiped-shaped layer. The pattern 32 establishes two separatewinding or zig zag or inter-digitized fingers paths 34, 36 that areestablished without electrical connection between them, owing to thepattern 32. Each finger path 34, 36 is connected to a respectiveconductive lead 38, 40 as shown, with the leads 38, 40 being establishedby elongated legs of the sensing element pad 28 that extend away fromthe continuous area that bears the pattern 32. As shown at 42, thepattern 32 may begin at a location that is distanced from an edge 44 ofthe pad end of a conductive lead 38 to avoid tolerance stack-up

Turning now to FIG. 2, FIG. 2 shows an exploded view of a complete sootsensor 10. As shown, the sensing element pad 28 may be deposited onto amulti-layer substrate 30 made of, e.g., HTCC tape. A protective layer 46may be on the sensing element pad 28 as shown, and the ablating devicemay cut the pattern 32 in the protective layer 46, sensing element pad28, and even into the top layer 48 of the multi-layer substrate 30 asshown. A heater 50 with heater leads 52 may be deposited or formed on abottom layer 54 of the substrate 30 and covered with its own heaterprotective layer 56. The layers shown in FIG. 4 are substantially flushwith each other and coterminous with each other, except that the padprotective layer 46 might not extend all the way to the end of theelectrode legs 38, 40 of the sensing element pad 28 as shown.

FIG. 3 depicts an exemplary embodiment of an impedance measurementcircuit 60. As shown in FIG. 3, the first measuring lead 38 iselectrically communicated to a first lead 61. The first lead 61 extendsfrom the electrical communication with the first measuring lead 38 to aground potential 35. Additionally, a second lead 40 is electricallycommunicated to the second measuring lead 62. Optionally, a biasresistor 37 may be connected between leads 38 and 40 on the sensor inparallel with the sensing element electrodes in order to providecontinuous monitoring for any continuity loss in the vehicle/sensorharness. In an exemplary embodiment, resistor 37 may be formed of knownmaterials such as ruthenium oxide with a glass coating with post-elementfiring and laser trimmed. The second lead 62 extends from the electricalcommunication with the second measuring lead 40 to a resistor 33. Theresistor 33, in turn, is electrically communicated to a DC voltagesource 36, and to a measuring device 64. In an alternative exemplaryembodiment, the resistor 33 and measuring device 64 can be configuredwith lead 61 to be in electrical communication with ground potential 35.The measuring device 64 can be any device capable of reading theresistance, such as a voltmeter, or an ohmmeter.

The method and system of the invention may be used in conjunction with asensor for conductive particulate matter of any sort and in a variety ofenvironments. In one exemplary embodiment, the sensor is a soot sensorin the exhaust stream of an internal combustion engine such as a dieselengine. Referring now to FIG. 4, a non-limiting example of a particulatesensor diagnostic system 200 is illustrated. The diagnostic systemcomprises a controller or an engine control module (ECM) 202.Alternatively to an ECM, a stand-alone diagnostic or combined sensor anddiagnostic control module may be used, provided that it is able tocommunicate with an ECM in order to obtain information from the ECM,such as exhaust temperature, engine operating state, etc. ECM 202comprises among other elements a microprocessor for receiving signalsindicative of the vehicle performance as well as providing signals forcontrol of various system components, read only memory in the form of anelectronic storage medium for executable programs or algorithms andcalibration values or constants, random access memory and data buses forallowing the necessary communications (e.g., input, output and withinthe ECM) with the ECM in accordance with known technologies.

In accordance with an exemplary embodiment the controller will comprisea microcontroller, microprocessor, or other equivalent processing devicecapable of executing commands of computer readable data or program forexecuting a control algorithm. In order to perform the prescribedfunctions and desired processing, as well as the computations therefore(e.g., the control processes prescribed herein, and the like), thecontroller may include, but not be limited to, a processor(s),computer(s), memory, storage, register(s), timing, interrupt(s),communication interfaces, and input/output signal interfaces, as well ascombinations comprising at least one of the foregoing. For example, thecontroller may include input signal filtering to enable accuratesampling and conversion or acquisitions of such signals fromcommunications interfaces. As described above, exemplary embodiments ofthe present invention can be implemented through computer-implementedprocesses and apparatuses for practicing those processes.

The ECM receives various signals from various sensors in order todetermine the state of the engine as well as vary the operational stateand perform diagnostics for example, the ECM can determine, based on itsinput from other sensors 205 and logic and control algorithms whetherthe engine is being started in a “cold start” state as well as performand/or control other vehicle operations. Some of the sensors that may beincluded in other sensors 205 which provide input to the ECM 202 includebut are not limited to the following: engine coolant temperature sensor,engine speed sensor, exhaust oxygen sensor, engine temperature, and thelike. The sensors used may also be related in part to the type of enginebeing used (e.g., water cooled, air cooled, diesel, gas, hybrid, etc.).The ECM 202 also receives input from exhaust temperature sensor 215,which may be a temperature probe located in the exhaust stream inproximity to the particulate matter sensor or other equivalent means ormethod for measuring the exhaust temperature.

In accordance with operating programs, algorithms, look up tables andconstants resident upon the microcomputer of the ECM various outputsignals, including control of heater element 6 and diagnostic signal 220are provided by the ECM. While the control signals for heater element 6and diagnostic signal 220 are relevant to the practice of the invention,the ECM may also provide other control signals to control the engine(e.g., limiting or shutting off fuel flow as well as closing or openingthe intake and exhaust valves of the engine) as well as performing othervehicle operations including but not limited to: fuel/air flow controlto maintain optimum, lean or rich stoichiometry as may be required toprovide the required torque output; spark timing; engine output; andproviding on board malfunctioning diagnostic (OBD) means to the vehicleoperator.

Turning now to FIG. 5, a flow chart 300 illustrating portions of acontrol algorithm in accordance with an exemplary embodiment of theinvention is illustrated for performing diagnostics on a particulatematter sensor based on water vapor condensate. Here, control algorithm300 at step 302 determines whether a vehicle engine controlled by theECM is running, and the algorithm proceeds with the diagnostic only ifthe engine is running. If the engine is running, the algorithm indecision node 304 compares exhaust temperature from an exhausttemperature sensor against a predetermined value K_(start) _(—) _(temp),which is set at a level to determine whether the exhaust temperature istoo warm for water vapor condensate to be present on the particulatematter sensor. If the exhaust temperature is above K_(start) _(—)_(temp), then the algorithm determines that conditions are notsufficient for condensation to occur.

If, on the other hand, the algorithm determines at decision node 304that the exhaust temperature is not above K_(start) _(—) _(temp), thenthe diagnostic test proceeds to box 306 where an initial measurement ismade of resistance between the electrodes and a timer, utilizing aninternal clock of the ECM, is started. In decision node 308, thealgorithm compares this resistance measurement against a predeterminedvalue K_(init-thresh), which is set at a level below which it is likelythere is particulate matter or water vapor already present on theelectrodes of the sensor at the time the algorithm is initiated. If themeasured resistance is not greater than K_(R) _(—) _(init-thresh), thenthe algorithm assumes that either condensate or particulate matter isalready present between the electrodes, and the algorithm proceeds aheadto box 318, which will be described below.

If the measured resistance remains greater than K_(R) _(—)_(init-thresh) for a period long enough to ensure that the signal is notnoise or a signal spike (e.g., 3 seconds), then the algorithm proceedsto box 310 as the first step of a condensate detection decision loop.This decision loop is based on an observation made in the development ofthis invention that following startup of a cold engine, componentsupstream of the particulate matter sensor may not initially be warmenough (e.g., 40° C.) to maintain water in the exhaust stream in a vaporstate. In other words, water vapor in the exhaust stream may becondensing on components upstream of the particulate matter sensor sothat there is no water vapor left to condense on the particulate mattersensor. As the upstream components warm up from exposure to heatedexhaust gas, water vapor can be carried forward to the particulatematter sensor. At the same time, since it is further downstream, theparticulate matter sensor may still be cool enough (e.g., 40° C. orbelow) for this water vapor to condense on the particulate mattersensor. Therefore, in decision node 312, the algorithm compares theresistance measured in box 310 to a predetermined value K_(R) _(—)_(cond) _(—) _(thresh) for a period long enough to ensure that thesignal is not noise or a signal spike (e.g., 3 seconds), which is set ata level below which it is likely that there is water vapor condensatebetween the electrodes. If the resistance is not less than thepredetermined value K_(R) _(—) _(cond) _(—) _(thresh), then thealgorithm proceeds to decision node 314 and compares the elapsed time onthe timer that was started in box 306 the clock re-zeroed in box againsta predetermined value K_(cond) _(—) _(cold) _(—) _(time), which is setat a level beyond which it is unlikely that water vapor will condensebetween the electrodes. If the elapsed time is greater than thepredetermined value K_(cond) _(—) _(cold) _(—) _(time), then thealgorithm times out and determines that it was unable to detect thepresence of condensate. If the elapsed time is not greater than thepredetermined value K_(cond) _(—) _(cold) _(—) _(time), then thealgorithm returns to box 310 for a new measurement of resistance and acontinuation of the decision loop.

If the algorithm determines in decision node 312 that the resistancemeasured in box 310 is less than the predetermined value K_(R) _(—)_(cond) _(—) _(thresh), then the algorithm proceeds either to box 318where another resistance measurement is taken as the first step of acondensate evaporation detection decision loop if the algorithm is goingto wait for condensate to evaporate on its own (e.g., in response toheat from the heated exhaust stream), or optionally to box 316 where theheater element on the particulate matter sensor is turned on beforeproceeding to box 318 for the resistance measurement if the algorithm isgoing to utilize heater element heat to accelerate the evaporation ofcondensate.

After the resistance measurement is taken in box 318, the algorithmproceeds to decision node, where the resistance measurement from box318, is compared to a predetermined value K_(R) _(—) _(evap) _(—)_(thresh), which is set at a value above which it would indicate thatany condensate present between the electrodes has evaporated. If theresistance is not greater than the predetermined value K_(R) _(—)_(evap) _(—) _(thresh), then the algorithm proceeds to decision node 322and compares the elapsed time on the timer, which was re-started in box316 against a predetermined value K_(cond) _(—) _(evap) _(—) _(time),which is set at a level beyond which any condensate between theelectrodes would have likely evaporated. If the elapsed time is greaterthan the predetermined value K_(cond) _(—) _(evap) _(—) _(time), thenthe algorithm times out and determines that it was unable to confirm theevaporation of condensate. This determination could indicate theexistence of a fault condition in the sensor, but it could be becausethe low resistance measurements were due to particulate matter betweenthe electrodes and not condensate. If the elapsed time is not greaterthan the predetermined value K_(cond) _(—) _(evap) _(—) _(time), thenthe algorithm returns to box 318 for a new measurement of resistance anda continuation of the decision loop.

If the algorithm determines in decision node 320 that the resistancemeasured in box 318 is greater than the predetermined value K_(R) _(—)_(evap) _(—) _(thresh) for a period long enough to ensure that thesignal is not noise or a signal spike (e.g., 3 seconds), then thealgorithm proceeds to box 324 where the algorithm determines thatevaporation of condensate was confirmed, and validation signal that thesensor is in proper working order is diagnosed and reported to thesystem diagnostic function of the ECM. The algorithm then proceeds tobox 326 where the elapsed time on the timer, which had been re-startedin box 324 is compared to a predetermined value K_(postheat) _(—)_(time), which is set a period of time to ensure that water does notre-condense on the element. If the elapsed time is not greater thanK_(postheat) _(—) _(time), the algorithm simply waits until the timelimit is reached, after which the heater is turned off and thediagnostic algorithm is concluded.

In the cases where the algorithm 300 determines from decision node 304or decision node 314 that no condensate is present, or where itdetermines from decision node 322 that condensate evaporation cannot beconfirmed, the algorithm is unable to either validate or diagnose afailure of the particulate matter sensor. In some exemplary embodimentsof the invention, this simply results in a report to the systemdiagnostic function of the ECM that a definitive diagnosis could not bemade. In other exemplary embodiments, the ECM may then implement asecondary diagnostic function, for example, as described in US Pat. App.Publ. No. 2009/0090622 A1.

Another example of a second diagnostic function is an algorithm based ondetection of a change in the conductivity of the sensor substrate inresponse to heating, as disclosed in the U.S. patent application Ser.No. 12/614,654, filed Nov. 9, 2009 and entitled “Method and System forHeater Signature Detection Diagnostics of a Particulate Matter Sensor”filed on even date herewith. Sensor substrates whose electricalconductivity varies with temperature include, for example alumina,zirconia, yttria, lanthanum oxide, silica, or combinations of two ormore of any of the foregoing, containing glass additives such as SiO₂,Al₂O₃, B₂O₃, La₂O₃, or Y₂O₃. Exemplary amounts in which glass additivesmay be present in order to provide temperature-based resistancevariations may range from 0.1% to 12%.

Turning now to FIG. 6, a flow chart 400 illustrating portions of acontrol algorithm in accordance with an exemplary embodiment of theinvention is illustrated for performing level diagnostics on aparticulate matter sensor based on response to heating of the sensorsubstrate. In this exemplary embodiment, control algorithm 400 isimplemented as a secondary diagnostic as a result of a no condensatedetermination from decision nodes 304 or 314 or a no confirmation ofcondensate removal from decision node 322.

The first step of the diagnostic routine is to measure the resistancebetween the sensor electrodes in box 404 and store the value in the ECMas R_(OBD) _(—) _(init). The algorithm logic path then moves to decisionnode 406 where the algorithm assesses whether conditions are withinlimits for a heater-based regeneration of the particulate matter tooccur. The purpose of this assessment is to ensure that the conditionsare satisfactory for the rigorous heating used to induce a measurableelectrical conductivity change in the substrate. Such a heating profilemay be similar or identical to the heating profile used to burn offaccumulated particulate matter during a sensor regeneration. Thecriteria used to assess whether the conditions are satisfactory mayinclude (but are not limited to): an upstream diesel particulate filter(DPF) not being in regeneration mode itself (as such a regeneration incombination with activation of the heater in the heater signaturedetection particulate matter sensor diagnostic may cause overheating ofthe sensor, and also regeneration of the DPF could cause discharge ofcontaminants from the DPF that could interfere with the particulatematter sensor diagnostic) and/or the air flow exhaust flow volumes notbeing too high for the heater to sufficiently regenerate (e.g., 75m/sec) or too low so as to risk damage to the heater circuit (e.g., 5m/sec). If the criteria in decision node 406 are not met, the algorithmholds until they are met. Once the criteria in decision node 406 havebeen met, the algorithm moves on to box 408 to continue the diagnostic.

In box 408, the algorithm turns on the sensor heater and starts a timerusing an internal clock of the ECM. In box 408, the heater is initiallypowered according to a profile where the heat generated is sufficient toevaporate any liquid water such as water vapor condensate that mayhappen to be present between the electrodes, but not so great as tocause cracking or other damage to the sensor substrate as could happenif high heat were applied before condensate had evaporated. Once gradualheating has been applied long enough to drive off any condensate,greater amounts of heat, sufficient to induce an electrical conductivitychange in the substrate, are applied. In one exemplary embodiment wherethe substrate is an alumina substrate containing approximately 4% SiO₂glass additive(s), the heat is sufficient to induce a temperaturebetween about 500° C. and 800° C., as measurable reductions in theresistance of such materials are observed as temperatures approach andexceed 500° C., and 800° C. is close to the maximum temperatureachievable by an exemplary heater.

After box 408, the algorithm proceeds to box 409, which begins adecision loop where the resistance between the electrodes is observed tosee if it changes in a manner consistent with the heating of the sensorelement. In box 409, resistance between the sensor electrodes ismeasured and the resulting value is saved as R_(OBD) _(—) _(hot), andthe algorithm moves on to decision node 410.

In decision node 410, the algorithm evaluates the difference between themeasured resistance value R_(OBD) _(—) _(hot) and a predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) (e.g., 80%) ofR_(OBD) _(—) _(init). If R_(OBD) _(—) _(hot) is not less than thepredetermined percentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) ofR_(OBD) _(—) _(init), then the algorithm proceeds to decision node 412and compares the elapsed time on the timer that was started in box 408against a predetermined value K_(OBD) _(—) _(on) _(—) _(time), which isset at a level beyond which the heat being applied according to theprofile specified for box 408 should have induced the expected change inelectrical conductivity. If the elapsed time is greater than thepredetermined value K_(OBD) _(—) _(on) _(—) _(time), then the algorithmtimes out and diagnoses a sensor fault. If the elapsed time is notgreater than the predetermined value K_(OBD) _(—) _(on) _(—) _(time),then the algorithm returns to box 409 for a new measurement ofresistance and a continuation of the decision loop.

If the measured resistance value R_(OBD) _(—) _(hot) is less than thepercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init) in decision node 410, then the algorithm proceeds to box 414where the sensor heater is turned off so that the sensor can cool down.The algorithm then proceeds to box 416 where resistance between theelectrodes is measured and the value stored as R_(OBD) _(—) _(cold).

Box 416 also begins a decision loop where the resistance between theelectrodes is observed to see if it changes in a manner consistent withthe cooling of the sensor that is expected to occur after the sensorheater element is turned off in box 414. From box 416, the algorithmproceeds to decision node 418, where the algorithm evaluates thedifference between the measured resistance value R_(OBD) _(—) _(cold)and a predetermined percentage (e.g., 95%) of R_(OBD) _(—) _(init), andif that difference is not greater than the predetermined percentageK_(R) _(—) _(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init), thenthe algorithm proceeds to decision node 420 and compares the elapsedtime on the timer, which was re-started in box 414, against apredetermined value K_(OBD) _(—) _(off) _(—) _(time), which is set at alevel beyond which the sensor should have cooled sufficiently formeasured resistance to approach R_(OBD) _(—) _(init) within the desiredlimits. If the elapsed time is greater than the predetermined valueK_(OBD) _(—) _(off) _(—) _(time), then the algorithm times out anddiagnoses a sensor fault. If the elapsed time is not greater than thepredetermined value K_(OBD) _(—) _(on) _(—) _(time), then the algorithmreturns to box 416 for a new measurement of resistance and acontinuation of the decision loop.

If the measured resistance value R_(OBD) _(—) _(cold) is greater thepercentage K_(R) _(—) _(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—)_(init) in decision node 418, then the algorithm diagnoses a validationthat the sensor is in proper working order and reports the same to theECM system diagnostic function.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description.

1. A method of diagnosing an operating condition of an electricallyconductive particulate matter sensor, said sensor comprising a substrateand two electrodes on said substrate adapted to collect particulatematter between the electrodes, thereby establishing an electricallyconductive path through collected particulate matter between theelectrodes that can be detected by measuring electrical resistancebetween the electrodes, R_(elect), said method comprising the steps of:(a) detecting whether water vapor condensate may be present between theelectrodes; (b) if water vapor condensate may be present between theelectrodes, subjecting the sensor to conditions sufficient to evaporateany water vapor condensate, and detecting whether R_(elect) increases ina manner consistent with evaporation of water vapor condensate; (c) ifstep (b) detects that water vapor condensate may be present, and ifR_(elect) increases in a manner consistent with evaporation of watervapor condensate in response to the sensor being subjected to conditionssufficient to evaporate any water vapor condensate, then diagnosing avalidation that the sensor is in proper working condition.
 2. A methodaccording to claim 1 wherein step (a) comprises the steps of: (1)measuring temperature of an exhaust gas flowing past the sensor; (2) ifthe exhaust temperature is above a predetermined value K_(start) _(—)_(temp), determining that water vapor condensate is not present; and (3)if the exhaust temperature is not above K_(start) _(—) _(temp),determining that water vapor condensate may be present.
 3. A methodaccording to claim 2, further comprising the step: (4) if the exhausttemperature is not above K_(start) _(—) _(temp), then (i) measuringR_(elect); (ii) determining whether R_(elect) is below a predeterminedvalue K_(R) _(—) _(cond) _(—) _(thresh); and (iii) continuing to measureR_(elect) for a period of time; (5) if R_(elect) falls below K_(R) _(—)_(cond) _(—) _(thresh) during said period of time, then determining thatwater vapor condensate may be present; and (6) if R_(elect) does notfall below K_(R) _(—) _(cond) _(—) _(thresh) during said period of time,then determining that water vapor condensate is not present.
 4. A methodaccording to claim 3 wherein a heater element disposed in the sensor isa source of heat applied to the sensor in step (b).
 5. A methodaccording to claim 1 wherein heat is applied to the sensor in step (b)to accelerate the evaporation of water vapor condensate.
 6. A methodaccording to claim 5 wherein step (b) comprises the steps of: (1)measuring R_(elect); (2) determining whether R_(elect) is above apredetermined value K_(R) _(—) _(evap) _(—) _(thresh); (3) continuing tomeasure R_(elect) for a period of time; (4) if R_(elect) does not riseabove K_(R) _(—) _(evap) _(—) _(thresh) during said period of time, thendetermining that evaporation of condensate could not be confirmed; and(5) if R_(elect) rises above K_(R) _(—) _(evap) _(—) _(thresh) duringsaid period of time, then diagnosing a validation condition that thesensor is in proper working condition.
 7. A method according to claim 1,wherein said sensor comprises a heater element disposed therein andwherein said substrate has an electrical conductivity that varies withtemperature, said method further comprising the steps of: (d) if watervapor is not detected between the electrodes in step (a), or ifR_(elect) does not increase in a manner consistent with evaporation ofwater vapor condensate in step (b), then providing heat to the sensor inan amount sufficient to modify the electrical resistance of thesubstrate, and detecting whether R_(elect) changes in a mannerconsistent with heating of the substrate; (e) if R_(elect) increases ina manner consistent with heating of the substrate in step (d), thenremoving the heat provided in step (d) to cool the substrate; (f) ifR_(elect) does not change in a manner consistent with heating of thesubstrate in step (d) or R_(elect) does not change in a mannerconsistent with cooling of the substrate in step (e), then diagnosing afailure condition for the sensor; and (g) if R_(eject) changes in amanner consistent with cooling of the substrate in step (e), thendiagnosing a validation that the sensor is in proper working condition.8. A method according to claim 7 wherein step (d) comprises the stepsof: (1) measuring R_(elect) and storing the value as R_(OBD) _(—)_(init); (2) activating the heater element for a first period of time;while periodically measuring R_(elect), and storing the value as R_(OBD)_(—) _(hot); (3) comparing R_(OBD) _(—) _(hot) a predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init); (4) if R_(OBD) _(—) _(hot) is not less than the predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init), then determining that R_(elect) did not change in a mannerconsistent with heating the substrate; and (5) if R_(OBD) _(—) _(hot) isless than the predetermined percentage K_(R) _(—) _(OBD) _(—) _(on) _(—)_(pct) of R_(OBD) _(—) _(init) as determined in step (3) during saidfirst period of time, then determining that R_(elect) changed in amanner consistent with heating the substrate.
 9. A method according toclaim 8 wherein step (e) comprises the steps of: (1) deactivating theheater for a second period of time while periodically measuringR_(ejlct), and storing the value as R_(OBD) _(—) _(cold); (2) comparingR_(OBD) _(—) _(cold) to a predetermined percentage K_(R) _(—) _(OBD)_(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init); (3) if R_(OBD) _(—)_(cold) is not greater than the predetermined percentage K_(R) _(—)_(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init) during saidsecond period of time, then determining that R_(elect) did not change ina manner consistent with heating the substrate; and (4) if R_(OBD) _(—)_(cold) is greater than the predetermined percentage K_(R) _(—) _(OBD)_(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init) during said secondperiod of time, then determining that R_(elect) did change in a mannerconsistent with heating the substrate.
 10. A method of diagnosing anoperating condition of an electrically conductive particulate mattersensor, said sensor comprising a substrate having an electricalresistance that varies with temperature, two electrodes on saidsubstrate adapted to collect particulate matter between the electrodes,thereby establishing an electrically conductive path through collectedparticulate matter between the electrodes that can be detected bymeasuring electrical resistance between the electrodes, R_(elect), and aheater element adapted to heat an area between said electrodes, saidmethod comprising the steps of: (a) detecting whether water vaporcondensate may be present between the electrodes by: (1) measuringtemperature of an exhaust gas flowing past the sensor; (2) if theexhaust temperature is above a predetermined value K_(start) _(—)_(temp), determining that water vapor condensate is not present; and (3)if the exhaust temperature is not above K_(start) _(—) _(temp),determining that water vapor condensate may be present. (4) if theexhaust temperature is not above K_(start) _(—) _(temp), then (i)measuring R_(elect); (ii) determining whether R_(elect) is below apredetermined value K_(R) _(—) _(cond) _(—) _(thresh); and (iii)continuing to measure R_(elect) for a first period of time; (5) ifR_(elect) falls below K_(R) _(—) _(cond) _(—) _(thresh) during saidfirst period of time, then determining that water vapor condensate maybe present; and (6) if R_(elect) does not fall below K_(R) _(—) _(cond)_(—) _(thresh) during said first period of time, then determining thatwater vapor condensate is not present; (b) if step (a) determines thatwater vapor condensate may be present between the electrodes, thensubjecting the sensor to conditions sufficient to evaporate any watervapor condensate, and diagnosing a validation that the sensor is inproper operating condition if R_(elect) increases in a manner consistentwith evaporation of water vapor condensate; (c) if water vapor is notdetected between the electrodes in step (a), or if R_(elect) does notincrease in a manner consistent with evaporation of water vaporcondensate in step (b), then (1) measuring R_(elect) and storing thevalue as R_(OBD) _(—) _(init); (2) activating the heater element for asecond period of time; while periodically measuring R_(elect) andstoring the value as R_(OBD) _(—) _(hot); (3) comparing R_(OBD) _(—)_(hot) a predetermined percentage K_(R) _(—) _(OBD) _(—) _(on) _(—)_(pct) of R_(OBD) _(—) _(init); (4) if R_(OBD) _(—) _(hot) is not lessthan the predetermined percentage K_(R) _(—) _(OBD) _(—) _(on) _(—)_(pct) of R_(OBD) _(—) _(init), then diagnosing a failure condition forthe sensor; (d) if the comparison in step (c)(3) results in adetermination that R_(OBD) _(—) _(hot) is less than the predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init), then: (1) deactivating the heater for a third period of timewhile periodically measuring R_(elect), and storing the value as R_(OBD)_(—) _(cold); (2) comparing R_(OBD) _(—) _(cold) to a predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—)_(init); (3) if R_(OBD) _(—) _(cold) is not greater than thepredetermined percentage K_(R) _(—) _(OBD) _(—) _(off) _(—) _(pct) ofR_(OBD) _(—) _(init) during said third period of time, then diagnosing afailure condition for the sensor; and (4) if R_(OBD) _(—) _(cold) isgreater than the predetermined percentage K_(R) _(—) _(OBD) _(—) _(off)_(—) _(pct) of R_(OBD) _(—) _(init) during said third period of time,then determining that R_(elect), then diagnosing a validation that thesensor is in proper operating condition.
 11. A diagnostic system for anelectrically conductive particulate matter sensor comprising a substrateand two electrodes on said substrate adapted to collect particulatematter between the electrodes, thereby establishing an electricallyconductive path through collected particulate matter between theelectrodes that can be detected by measuring electrical resistancebetween the electrodes, R_(elect), said system comprising amicroprocessor in communication with the sensor and a storage mediumincluding instructions for causing the microprocessor to implement amethod comprising: (a) detecting whether water vapor condensate may bepresent between the electrodes; (b) if water vapor condensate may bepresent between the electrodes, subjecting the sensor to conditionssufficient to evaporate any water vapor condensate, and detectingwhether R_(elect) increases in a manner consistent with evaporation ofwater vapor condensate; (c) if step (b) detects that water vaporcondensate may be present, and if R_(elect) increases in a mannerconsistent with evaporation of water vapor condensate in response to thesensor being subjected to conditions sufficient to evaporate any watervapor condensate, then diagnosing a validation that the sensor is inproper working condition.
 12. A diagnostic system according to claim 11wherein step (a) comprises the steps of: (1) measuring temperature of anexhaust gas flowing past the sensor; (2) if the exhaust temperature isabove a predetermined value K_(start) _(—) _(temp), determining thatwater vapor condensate is not present; and (3) if the exhausttemperature is not above K_(start) _(—) _(temp), determining that watervapor condensate may be present.
 13. A diagnostic system according toclaim 12, wherein said method further comprising the steps: (4) if theexhaust temperature is not above K_(start) _(—) _(temp), then (i)measuring R_(elect); (ii) determining whether R_(elect) is below apredetermined value K_(R) _(—) _(cond) _(—) _(thresh); and (iii)continuing to measure R_(elect) for a period of time; (5) if R_(elect)falls below K_(R) _(—) _(cond) _(—) _(thresh) during said period oftime, then determining that water vapor may be present; and (6) ifR_(elect) does not fall below K_(R) _(—) _(cond) _(—) _(thresh) duringsaid period of time, then determining that water vapor is not present.14. A diagnostic system according to claim 11 wherein heat is applied tothe sensor in step (b) to accelerate the evaporation of water vaporcondensate.
 15. A diagnostic system according to claim 14 wherein aheater element disposed in said sensor is a source of heat applied tothe sensor in step (b).
 16. A diagnostic system according to claim 11wherein said sensor comprises a heater element disposed therein andwherein said substrate has an electrical conductivity that varies withtemperature, said method further comprising the steps of: (d) if watervapor is not detected between the electrodes in step (a), or ifR_(elect) does not increase in a manner consistent with evaporation ofwater vapor condensate in step (b), then providing heat to the sensor inan amount sufficient to modify the electrical resistance of thesubstrate, and detecting whether R_(elect) changes in a mannerconsistent with heating of the substrate; (e) if R_(elect) increases ina manner consistent with heating of the substrate in step (e), thenremoving the heat provided in step (d) to cool the substrate; (f) ifR_(elect) does not change in a manner consistent with heating of thesubstrate in step (d) or R_(elect) does not change in a mannerconsistent with cooling of the substrate in step (e), then diagnosing afailure condition for the sensor; and (g) if R_(elect) changes in amanner consistent with cooling of the substrate in step (e), thendiagnosing a validation that the sensor is in proper working condition.17. A diagnostic system according to claim 16 wherein step (d) comprisesthe steps of: (1) measuring R_(elect) and storing the value as R_(OBD)_(—) _(init); (2) activating the heater element for a first period oftime; while periodically measuring R_(elect), and storing the value asR_(OBD) _(—) _(hot); (3) comparing R_(OBD) _(—) _(hot) a predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init); (4) if R_(OBD) _(—) _(hot) is not less than the predeterminedpercentage K_(R) _(—) _(OBD) _(—) _(on) _(—) _(pct) of R_(OBD) _(—)_(init), then determining that R_(elect) did not change in a mannerconsistent with heating the substrate; and (5) if R_(OBD) _(—) _(hot) isless than the predetermined percentage K_(R) _(—) _(OBD) _(—) _(on) _(—)_(pct) of R_(OBD) _(—) _(init) as determined in step (3) during saidfirst period of time, then determining that R_(elect) changed in amanner consistent with heating the substrate.
 18. A diagnostic systemaccording to claim 17 wherein step (e) comprises the steps of: (6)deactivating the heater for a second period of time while periodicallymeasuring R_(elect), and storing the value as R_(OBD) _(—) _(cold); (7)comparing R_(OBD) _(—) _(cold) to a predetermined percentage K_(R) _(—)_(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init); (8) if R_(OBD)_(—) _(cold) is not greater than the predetermined percentage K_(R) _(—)_(OBD) _(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init) during saidsecond period of time, then determining that R_(elect) did not change ina manner consistent with heating the substrate; and (9) if R_(OBD) _(—)_(cold) is greater than the predetermined percentage K_(R) _(—) _(OBD)_(—) _(off) _(—) _(pct) of R_(OBD) _(—) _(init) during said secondperiod of time, then determining that R_(elect) did change in a mannerconsistent with heating the substrate.